The invention is related to the field of hermetic barrier layers in integrated circuits, in particular, silicon carbide barrier layers.
Statement of the Problem
There is a need in integrated circuits for hermetic barrier layers having low dielectric constants. When silicon carbide, SiC, is used as a barrier to protect underlying films in integrated circuit devices, moisture penetration through the silicon carbide needs to be minimized. SiC films prepared by conventional PECVD methods show an abundance of Sixe2x80x94H and Sixe2x80x94(CH3)x in the films, leading to moisture permeability of the SiC films. The problem is attributable mainly to the low film density caused by bulky xe2x80x94(CH3) groups, which generate large free volume inside the films and lead to ambient moisture penetration. Attempts in the prior art to increase hermeticity of barrier films often result in films having high dielectric constants, for example, of about 6.
The invention helps to solve some of the problems mentioned above by providing methods for fabricating a silicon carbide layer on an integrated circuit having good moisture-barrier properties and a low dielectric constant. A silicon carbide layer fabricated in accordance with the invention typically has a dielectric constant in a range of about from 4 to 5.
In one basic embodiment, the invention provides a plasma-enhanced method for depositing nitrogen-doped silicon carbide on an integrated circuit substrate. In one aspect, a method comprises flowing gaseous organosilane molecules into a reaction chamber. In another aspect, gaseous nitrogen-containing doping molecules are flowed into the reaction chamber. In another aspect, a gas plasma is formed in the reaction chamber. Preferably, the organosilane molecules comprise molecules having no Sixe2x80x94H bonds. Most preferably, the organosilane molecules comprise tetramethyl silane.
In another aspect, the doping molecules are selected from the group consisting of nitrogen gas, N2, and ammonia gas, NH3. Preferably, the flowrate of doping molecules into the reaction chamber is more than four times greater than the organosilane flowrate. In another aspect, a method in accordance with the invention comprises applying a low-frequency radio-frequency (xe2x80x9crfxe2x80x9d) bias to the substrate. In still another aspect, the applied bias has a frequency in a range of about from 100 kHz to 600 kHz. In another aspect, a method comprises a step of the applying a low-frequency rf bias to the substrate at a power in a range of about from 200 to 2000 Watts. Preferably, the low-frequency rf bias has a frequency of about 250 kHz and is applied in a range of about from 300 to 600 Watts.
In another aspect, forming a gas plasma comprises applying high-frequency radio frequency power to the reaction chamber. In still another aspect, applying high-frequency power comprises applying power having a frequency in a range of about from 10 MHz to 30 MHz, preferably about 13.6 MHz. In another aspect, applying high-frequency rf power comprises applying power in a range of about from 200 to 4000 watts. Preferably, power is applied in a range of about from 300 to 1400 watts to form a plasma.
In another aspect, a method in accordance with the invention comprises a step of maintaining the reaction chamber at a pressure in a range of about from 0.8 to 10 Torr. Preferably, the reaction chamber is maintained at a pressure in a range of about from 3 to 5 Torr. In another aspect, a method in accordance with the invention comprises a step of maintaining the reaction chamber at a temperature in a range of about from 200xc2x0 to 600xc2x0 C. Preferably, the reaction chamber is maintained at a temperature in a range of about from 350xc2x0 to 425xc2x0 C.
Another basic embodiment of a method in accordance with the invention provides a plasma-enhanced method for depositing oxygen-doped silicon carbide on an integrated circuit substrate. In one aspect, a method comprises flowing gaseous organosilane molecules into a reaction chamber. In another aspect, gaseous oxygen-containing doping molecules are flowed into the reaction chamber. In still another aspect, a gas plasma is formed in the reaction chamber. In still another aspect, the organosilane molecules comprise molecules having no Sixe2x80x94H bonds. Preferably, the organosilane molecules comprise tetramethyl silane.
In another aspect, the doping molecules comprise a weak oxidizer. In another aspect, the doping molecules comprise carbon dioxide, CO2. In another aspect, weak-oxidizer oxygen doping molecules are flowed into the reaction chamber at a doping flowrate more than four times greater than the organosilane flowrate.
In another aspect, a method comprises the step of applying a low-frequency rf bias to the substrate, preferably at a frequency in a range of about from 100 kHz to 600 kHz. In another aspect, a low-frequency rf bias is applied to the substrate at a power in a range of about from 200 to 2000 Watts. In another aspect, a low-frequency rf bias is applied to the substrate at a frequency of about 250 kHz in a range of about from 400 to 800 Watts.
In another aspect, applying high-frequency rf power comprises applying power in a range of about from 200 to 4000 watts, preferably in a range of about from 300 to 1400 watts. In still another aspect, the reaction chamber is maintained at a pressure in a range of about from 0.8 to 10 Torr, preferably at a pressure in a range of about from 1.5 to 3 Torr. In another aspect, the reaction chamber is maintained at a temperature in a range of about from 200xc2x0 to 600xc2x0 C., preferably in a range of about from 350xc2x0 to 425xc2x0 C.
In still another aspect, a method for depositing oxygen-doped silicon carbide comprises flowing oxygen doping molecules comprising a strong oxidizer, such as oxygen gas, (O2) nitrous oxide (N2O), and ozone (O3). In still another aspect, the step of flowing doping molecules into the reaction chamber comprises flowing oxygen doping molecules at a doping flowrate about the same or less than the organosilane flowrate.
A third basic embodiment of a method in accordance with the invention provides a plasma-enhanced method for depositing doped silicon carbide containing both nitrogen dopant and oxygen dopant. In one aspect, gaseous organosilane molecules are flowed into a reaction chamber. In another aspect, gaseous nitrogen doping molecules and oxygen doping molecules are flowed into the reaction chamber. In another aspect, a gas plasma is formed in the reaction chamber.
In another aspect, the organosilane molecules comprise molecules having no Sixe2x80x94H bonds. Preferably, the organosilane molecules comprise tetramethyl silane. In another aspect, the nitrogen doping molecules are selected from the group consisting of nitrogen gas, N2, and ammonia gas, NH3, and the oxygen doping molecules comprise a weak oxidizer, for example, carbon dioxide, CO2. In another aspect, the step of flowing the nitrogen doping molecules and weak-oxidizer oxygen doping molecules into the reaction chamber comprises flowing the doping molecules at a doping flowrate more than four times greater than the organosilane flowrate.
In another aspect, the nitrogen doping molecules are selected from the group consisting of nitrogen gas, N2, and ammonia gas, NH3, and the oxygen doping molecules comprise a strong oxidizer, for example, oxygen gas, (O2), nitrous oxide (N2O), and ozone (O3). In another aspect, the step of flowing the nitrogen doping molecules and strong-oxidizer oxygen doping molecules into the reaction chamber comprises flowing the nitrogen doping molecules at a nitrogen doping flowrate more than two times greater than the organosilane flowrate, and flowing the strong-oxidizer oxygen doping molecules at an oxygen doping flowrate about the same or less than the organosilane flowrate.
In another aspect, a low-frequency rf bias is applied to the substrate. In another aspect, the low-frequency rf bias is applied at a frequency in a range of about from 100 kHz to 600 kHz. In still another aspect, the low-frequency rf bias is applied at a power level in a range of about from 200 to 2000 Watts. In another aspect, the step of applying a low-frequency rf bias to the substrate comprises applying a bias at a frequency of about 250 kHz in a range of about from 300 to 600 Watts. In another aspect, forming a gas plasma comprises applying high-frequency rf power to the reaction chamber. In another aspect, applying high-frequency rf power comprises applying power having a frequency in a range of about from 10 MHz to 30 MHz, preferably about 13.6 MHz. In another aspect, applying high-frequency rf power comprises applying power in a range of about from 200 to 4000 watts. In another aspect, applying high-frequency rf power comprises applying power in a range of about from 300 to 1400 watts.
In another aspect, depositing a silicon carbide layer containing both nitrogen and oxygen dopant comprises maintaining the reaction chamber at a pressure in a range of about from 0.8 to 10 Torr, preferably in a range of about from 2 to 4 Torr. In another aspect, the reaction chamber is maintained at a temperature in a range of about from 200xc2x0 to 600xc2x0 C., preferably in a range of about from 350xc2x0 to 425xc2x0 C.